SIRT1 Undergoes Alternative Splicing in a Novel Auto-Regulatory Loop with p53

Abstract

BackgroundThe NAD-dependent deacetylase SIRT1 is a nutrient-sensitive coordinator of stress-tolerance, multiple homeostatic processes and healthspan, while p53 is a stress-responsive transcription factor and our paramount tumour suppressor. Thus, SIRT1-mediated inhibition of p53 has been identified as a key node in the common biology of cancer, metabolism, development and ageing. However, precisely how SIRT1 integrates such diverse processes remains to be elucidated.Methodology/Principal FindingsHere we report that SIRT1 is alternatively spliced in mammals, generating a novel SIRT1 isoform: SIRT1-ΔExon8. We show that SIRT1-ΔExon8 is expressed widely throughout normal human and mouse tissues, suggesting evolutionary conservation and critical function. Further studies demonstrate that the SIRT1-ΔExon8 isoform retains minimal deacetylase activity and exhibits distinct stress sensitivity, RNA/protein stability, and protein-protein interactions compared to classical SIRT1-Full-Length (SIRT1-FL). We also identify an auto-regulatory loop whereby SIRT1-ΔExon8 can regulate p53, while in reciprocal p53 can influence SIRT1 splice variation.Conclusions/SignificanceWe characterize the first alternative isoform of SIRT1 and demonstrate its evolutionary conservation in mammalian tissues. The results also reveal a new level of inter-dependency between p53 and SIRT1, two master regulators of multiple phenomena. Thus, previously-attributed SIRT1 functions may in fact be distributed between SIRT1 isoforms, with important implications for SIRT1 functional studies and the current search for SIRT1-activating therapeutics to combat age-related decline.

A Deacetylase-Deficient SIRT1 Variant Opposes Full-Length SIRT1 in Regulating Tumor Suppressor p53 and Governs Expression of Cancer-Related Genes

“…1A. Previously we reported a SIRT1 splice variant which lacked exon 8, termed SIRT1-⌬8 (33). In the course of cloning SIRT1-⌬8 (33), we reproducibly observed a 0.7-kb RNA species amplified by RT-PCR (Fig.…”

“…However, different groups, using different SIRT1 gene modifications and/or deletions, have reported variable effects of SIRT1 deficiency upon the degree of embryonic viability and development (13,34,54). This may be explained in part at least by the recent discovery that SIRT1 pre-mRNA is subject to alternative splicing (33), as different experimental SIRT1 deletions may fail to completely eradicate all SIRT1 isoforms.…”

“…The first reported SIRT1 splice variant, SIRT1-⌬8, lacks exon 8 due to in-frame splicing between exons 7 and 9 of full-length SIRT1 (SIRT1-FL) RNA (33). The novel SIRT1-⌬8 isoform displays distinct differences in stress-sensitivity, RNA/protein stability, protein-protein interactions, and deacetylase activity compared with SIRT1-FL.…”

“…The novel SIRT1-⌬8 isoform displays distinct differences in stress-sensitivity, RNA/protein stability, protein-protein interactions, and deacetylase activity compared with SIRT1-FL. Expression of SIRT1-⌬8 is stress responsive, p53 dependent, and conserved in mammals (33).…”

Sirtuin-1 Regulates Acinar-to-Ductal Metaplasia and Supports Cancer Cell Viability in Pancreatic Cancer

“…S7A and S7B). Using co-IP, we detected the Sirt1 isoform that has the highest deacetylase activity (29). As of b-catenin, 2 bands were detected (Fig.…”